private static async Task OnQueryReceived(object sender, QueryReceivedEventArgs e)
{
var message = e.Query as DnsMessage;
var response = message?.CreateResponseInstance();
if (message?.Questions.Count == 1)
{
// send query to upstream _servers
var question = message.Questions[0];
DnsClient client = DnsClient.Default;
if (FORCE_IPV4)
{
Random rand = new Random();
var ipv4DnsServers = DnsClient.GetLocalConfiguredDnsServers().Where(a => a.AddressFamily == System.Net.Sockets.AddressFamily.InterNetwork);
var list = ipv4DnsServers.OrderBy(a => rand.Next()).ToList();
client = new DnsClient(list, DnsClient.Default.QueryTimeout);
}
var upstreamResponse =
await client.ResolveAsync(question.Name, question.RecordType, question.RecordClass);
// if got an answer, copy it to the message sent to the client
if (upstreamResponse != null)
{
foreach (var record in (upstreamResponse.AnswerRecords))
{
response.AnswerRecords.Add(record);
}
foreach (var record in (upstreamResponse.AdditionalRecords))
{
response.AdditionalRecords.Add(record);
}
response.ReturnCode = ReturnCode.NoError;
// set the response
e.Response = response;
}
}
}
public static void Verify(MailAddress email)
{
// Try get SMTP server
var client = new DnsClient(DnsClient.GetLocalConfiguredDnsServers(), 1000);
var dnsMessage = client.Resolve(DomainName.Parse(email.Host), RecordType.Mx);
if (dnsMessage == null)
{
throw new TimeOutException("Operation has timed out!");
}
if (dnsMessage.ReturnCode == ReturnCode.NxDomain)
{
throw new NxDomainException("Domain not exists!");
}
if (dnsMessage.ReturnCode != ReturnCode.NoError)
{
throw new DomainValidationException("Unable to validate domain!");
}
if (!dnsMessage.AnswerRecords.Any())
{
throw new NoMxRecordException("No MX records!");
}
var mainServer = dnsMessage.AnswerRecords.OfType <MxRecord>().OrderBy(s => s.Preference).First();
// Try validate account
var smtpClient = new SimpleSmtpClient(mainServer.ExchangeDomainName.ToString(), _smtpPort);
var response = smtpClient.Read();
if (IsError(response.StatusCode))
{
throw new EmailValidationException($"Connection refused: {response.Description}");
}
response = smtpClient.SendCommand($"HELO {_identity}");
if (IsError(response.StatusCode))
{
throw new EmailValidationException($"Greeting failed: {response.Description}");
}
response = smtpClient.SendCommand($"VRFY {email.Address}");
if (!IsError(response.StatusCode))
{
return;
}
if (response.StatusCode == SmtpStatusCode.MailboxUnavailable)
{
throw new NxEmailException($"Email does not exists: {response.Description}");
}
response = smtpClient.SendCommand($"MAIL FROM:<{_sender}>");
if (IsError(response.StatusCode))
{
throw new EmailValidationException($"SMTP server is insane: {response.Description}");
}
response = smtpClient.SendCommand($"RCPT TO:<{email.Address}>");
if (IsError(response.StatusCode))
{
throw new NxEmailException($"Email is invalid: {response.Description}");
}
}
